[R-sig-Geo] spTransform: unable to convert coordinates

[Martin Ivanov]

Dear Prof. Bivand,

Here is a minimal working example with SpatialLines and SpatialPolygons. 
With both objects spTransform does not
multiply the transformed coordinates by 180/pi:

crds1 <- matrix(data=c(7, 51, 8, 52, 9, 52, 10, 51), ncol=2, byrow=TRUE, 
dimnames=list(NULL, c("lon", "lat")));
crds2 <- matrix(data=c(8, 48, 9, 49, 11, 49, 9, 48), ncol=2, byrow=TRUE, 
dimnames=list(NULL, c("lon", "lat")));
crds3 <- matrix(data=c(6, 47, 6, 55, 15, 55, 15, 47), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
spLines <- SpatialLines(list(Lines(list(Line(crds1), Line(crds2), 
Line(crds3)), ID="a")));
spLines at proj4string <- CRS("+proj=longlat +ellps=sphere +no_defs");
bbox(spLines);
spLines_tr <- spTransform(spLines, CRS("+proj=ob_tran +o_proj=longlat 
+o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +ellps=sphere +no_defs"), 
use_ob_tran=TRUE);
bbox(spLines_tr)
bbox(spLines_tr)*180/pi

crds1 <- matrix(data=c(7, 51, 8, 52, 9, 52, 10, 51, 7, 51), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds2 <- matrix(data=c(8, 48, 9, 49, 11, 49, 9, 48, 8, 48), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds3 <- matrix(data=c(6, 47, 6, 55, 15, 55, 15, 47, 6, 47), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
spPolygons <- SpatialPolygons(list(Polygons(list(Polygon(crds1), 
Polygon(crds2), Polygon(crds3)), ID="a")));
spPolygons at proj4string <- CRS("+proj=longlat +ellps=sphere +no_defs");
bbox(spPolygons);
spPolygons_tr <- spTransform(spPolygons, CRS("+proj=ob_tran 
+o_proj=longlat +o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +ellps=sphere 
+no_defs"), use_ob_tran=TRUE);
bbox(spPolygons_tr)
bbox(spPolygons_tr)*180/pi


The correct bounding boxes are the second ones. Hence the coordinates 
have also got to be multiplied by 180/pi.

Best regards,

Martin






On 08/23/2012 02:37 PM, Roger Bivand wrote:
> On Thu, 23 Aug 2012, Martin Ivanov wrote:
>
>> Dear Prof. Bivand,
>>
>> I tested spTransform with a SpatialLines object and it still does not 
>> multiply the coordinates by 180/pi. With SpatialPixels, SpatialPoints 
>> and SpatialGrids it works perfectly though. If necessary, I will 
>> provide a minimal working example.
>
> Please do - I may have left something out. I'm travelling now, so an 
> example would help. What about SpatialPolygons objects?
>
> Roger
>
>>
>> Best regards,
>>
>>
>


-- 
Dr. Martin Ivanov
Eberhard-Karls-Universität Tübingen
Mathematisch-Naturwissenschaftliche Fakultät
Fachbereich Geowissenschaften
Water & Earth System Science (WESS)
Hölderlinstraße 12, 72074 Tübingen, Deutschland
Tel. +4970712974213